c:\@Work\Perl\monks>perl -wMstrict -le
"use List::MoreUtils qw(uniq);
 use Data::Dump;
 ;;
 use constant DIPEPS   => qw(AA AL DA DE DV VD DW QD SD HD ED DY VE EN EI KE NV VP FV SS WK KK);
 use constant N_DIPEPS => scalar DIPEPS;
 ;;
 my ($dipep) =
   map  qr{ (?i) (?: $_) }xms,
   join '|',
   DIPEPS
   ;
 ;;
 my %count;
 for my $seq (qw(AAALVDENEC AATLVDEGDG)) {
   $count{$seq} = uniq $seq =~ m{ (?= ($dipep)) }xmsg;
   }
 dd \%count;
 ;;
 for my $seq (keys %count) {
   my $sum = $count{$seq};
   my $abs = N_DIPEPS - $sum;
   print qq{$seq: sum = $sum, abs = $abs};
   }
"
{ AAALVDENEC => 5, AATLVDEGDG => 3 }

AAALVDENEC: sum = 5, abs = 17
AATLVDEGDG: sum = 3, abs = 19